Gay

After the machine tech did an overhall on my machine and frame I have made and quilted two large quilts with no problems this year. Today we put my DDs masterpiece up and I find issues with the stitching on the back. Have played with the tensions, cleaned the bobbin and casing with no joy, and am at my wits' end. DD found a video that says something about a lip too close to the shuttle, but I can't see the connection to the problem, and don't know what to do with that either. Any suggestions?